sech(arctanh(x)*arctan(x))=1-12/4!*x^4-3248/8!*x^8-25240512/12!*x^12...

A012737

sech(arctanh(x)*arctan(x))=1-12/4!*x^4-3248/8!*x^8-25240512/12!*x^12...

Terms

    a(0) =1a(1) =-12a(2) =-3248a(3) =-25240512a(4) =-722745554688

External references